The purpose of this study is to determine the impact of lipid peroxide induced oxidative stress on individual tissues involved in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS). Many studies have suggested an important role for oxidative stress in ALS;however, the specific types of oxidative damage and the target cells that are important in ALS have not been elucidated. This information could be instrumental in helping to design much needed effective therapeutic interventions for this disease. In this proposal, we will test the hypothesis that an increase in lipid peroxides plays a critical role in the initiation and/or progression of ALS and that the cell types involved in the disease may be differentially affected. To do this, we will use a mouse model developed in our laboratory to manipulate the levels of lipid hydroperoxides, a conditional knockout mouse carrying floxed alleles for phospholipid hydroperoxide glutathione peroxidase (Gpx4flfl mice). Gpx4 plays a critical role in protecting membranes by removal of lipid hydroperoxides. We will measure the effect of increased lipid peroxides in specific tissues/cell types on disease initiation and progression by crossing the Gpx4flfl to mice carrying the G93AGur1 ALS mutant SOD1 transgene. Through targeted expression of Cre recombinase to specific tissues (e.g., motor neurons, skeletal muscle, microglia and astrocytes) in the Gpx4flfl conditional knockout ALS mutant mice, we will generate tissue-specific deletion of Gpx4, a key antioxidant enzyme, and increase lipid hydroperoxide induced oxidative stress in the targeted tissues/cell types. We will measure disease onset (loss of body weight and neurologic score), progression (rotarod, motor neuron numbers, loss of muscle innervation) and lifespan in wild type control mice, G93A1Gur transgenic mice, Gpx4flfl mice x tissue specific Cre mice and G93A1Gur Gpx4flfl x tissue specific Cre mice. We will also measure oxidative damage to lipid (F2-isoprostanes, neuroprostanes), DNA (oxo8dG) and protein (carbonyls, HNE adducts) in spinal cord and gastrocnemius muscle at pre-symptomatic, onset and end stages of the disease to determine the impact of increased oxidative stress on disease initiation and progression in these tissues. The studies we have proposed will increase our understanding of the effect of increased oxidative stress in general, and lipid peroxides in particular, in specific tissues/cells potentially involved in the initiation and progression of the neurodegenerative disease ALS. This novel approach to measure tissue specific effects of a specific type of oxidative damage has significant potential to generate information that will facilitate the design of effective treatments not only for ALS, but also for and other diseases involving motor neuron degeneration.